Dark halo merging and galaxy formation

This dissertation investigates several related aspects in the theory of hierarchical galaxy formation, using high resolution cosmological simulations and analytic and semi-analytic models for forming galaxies within dark-matter halos to make theoretical predictions that are closely tied to observations. I have concentrated primarily on two topics, both relating to the effect of merging on dark-matter halo properties and on mechanisms for galaxy formation.; Recent advances in observational techniques have aided in the discovery of a large population of high-redshift galaxies, identified using the Lyman-break technique. In Part I, I discuss how this population of Lyman-break galaxies (LBGs) can constrain models of structure formation and galaxy formation. N-body simulations are combined with semi-analytic models for populating high-redshift dark matter halos with LBGs. I examine scenarios in which high-redshift star formation is driven by collisional starbursts and scenarios in which quiescent star formation dominates, make predictions for the clustering properties of each model, and confront these predictions with the clustering properties of observed LBGs. I also present an analytic formalism that can be used to constrain the halo occupation function for a population galaxies, and discuss present constraints using observational quantities of LBGs. Models for high redshift halo occupation can be constrained using these methods but at present the data cannot rule out most realistic models.; In Part II, I discuss results from a structural merger tree derived from a high-resolution N-body simulation, which tracks the evolution of mass assembly histories and structural parameters for a statistical sample of dark-matter halos in a ΛCDM cosmology. Halo density profiles can be characterized by a concentration parameter, c_vir, which I show is inversely proportional to a scaled formation scale-factor which characterizes its mass assembly history. Scatter in c_vir for a given mass can be explained almost entirely by scatter in the characteristic formation epoch. This model can be used to predict the mass and redshift dependence of c_vir, and the scatter about these relations, using the extended Press-Schechter approximation. I also discuss how the build-up and evolution of a halo's angular momentum is related to its merging and accretion history, and show how the structural merger tree I have developed can be combined with semi-analytic models for galaxy formation to predict observable properties of galaxies.